Powder containing nitrocellulose, metal or metal hydride and a superficial layer of moderating agent



United States Patent 4 Claims. Cl. 149 13) ABSTRACT OF THE DISCLOSURE The present invention is directed to propulsive powders for mortar shells. The powder comprises a granular mixture of a major proportion of a propulsive organic nitrate preferably nitrocellulose and a powdered metal or metal compound such as aluminum, magnesium, beryllium, lithium and lithium hydride. The granular powder mixture in addition possesses a superficial layer of a moderator such as centralites, dinitrotoluene, camphor, diphenylamine and urethanes which is applied by a glossing technique. Preferred powders contain from 0.5 to by weight of the metal or metallic compound and from about 0.5% to 20% by weight of the moderator.

The firing of mortar shells is effected by ball-less cartridges, containing a propulsion powder charge enclosed in a case which is sealed by a mount folded in upon a sealing varnish. The pressure of the combustion gases acts upon the base of the mortar shell, the stern of which, pushed into the end of the tube, acts as a piston. Although the principle as such is thus very simple, it has always been extremely difiicult to make this system function in a convenient and reproducible manner.

The absence of a projectile set upon the case of the cartridge and limiting the expansion of the combustion gases in the mortar causes the creation of an undulatory pressure system which is responsible for the large variations in the values of the maximum pressures. Experimental measurements have shown that the wave has time to travel, out and back, two or three times the length of the tube before the mortar shell is expelled and no longer serves as a reflector. The amplitude of the wave diminishes rapidly with reflections, but during the first transit it is so high that it often involves rupture of the feathering of the mortar.

Also the powder is ignited inside the sealed cartridge. As the filling coeflicient (i.e. the ratio of the useful charge to the charge occupying the interior volume of the cartridge), of all kinds of mortar shell cartridges filled with known powders is not sufficient, ignition occurs under adverse conditions which is the cause of considerable variations of velocity and pressure. Moreover under the pressure of the gases produced by the powder on combustion, the forward end of the cartridge opens and the compressed gases escape into the tube. The sudden decompression which results inside the cartridge causes partial extinction to a greater or lesser extent of the powder when it is insufliciently ignited or when it has too low a resistance to extinction.

In order to remedy the extinction of a significant part of the powder, it has been proposed in French patent specification No. 1,311,647 to add to the powder a strongly exothermic reactant, such as paraphenylenediamine. But this additive alone, although it facilitates combustion of the powder does not provide for the propulsive unit a sufficiently regular and progressive combustion in order to impart the maximum impulse to the projectile.

The present invention has the object of providing a granular powder for mortar shell cartridges having the following characteristics:

Satisfactory ignition irrespective of the filling coefficient, the position of the powder charge in the case, and the initial temperature;

Higher resistance to extinction even under highly adverse conditions and with low initial temperatures;

Stea-diness of the manner in which the major part of the powder burns after opening of the cartridge and projection of the powder charge into the tube.

For this purpose the granular powder according to the invention is composed of a major part of nitrocellulose or an organic nitrate or a mixture of nitrocellulose and an organic nitrate and also contains:

(a) On the one hand, in a manner uniformly distributed throughout the mass, a metal or a metallic compound which is finely divided and is a good conductor of heat having a high energy of combustion and which ignites only in the gases at a temperature above a predetermined level which is a function of the nature of these gases, such as aluminium, magnesium, beryllium, lithium, lithium hydride or the like;

(b) On the other hand in a superficial layer in addition to the metal or metallic compound, a moderating agent which can be introduced by a glossing technique, such as centralites, particularly ethyl centralite, 2,4-dinitrotoluene and 2,6-dinitrotoluene, camphor, diphenylamine, urethanes and similar materials.

The thermal conductivity of the metals used is always much greater than that of the powders. As regards their energy of combustion, this can be characterised by the apparent potential of the metal which should be higher than that of the powder, the metals or metallic compound chosen having an apparent potential greater than 2000 cal./g.

The amount of metal or metallic compound can range from 0.5% to 10% according to the nature of the metal or metallic compound and the operating characteristics of the shell. However it should be sufiiciently high for the powder to have sufiicient properties of ignition and a resistance to extinction without being high enough for the combustion products to cause too large an erosive action on the mortar as a result of a high combustion temperature and the presence of solid compounds in the combustion products of the powder.

The amount of the moderator can range from O.520% according to the nature of the moderator and that of the metal or metallic compound introduced into the powder. It should always be sufficiently high for the combustion temperature of the superficial layer of the powder to be lower than the combustion threshold of the metal or the metallic compound contained in the powder. Also it should be sufiiciently low for the combustion temperature under constant volume of the superficial layer of the powder to be greater than 1800 K., the ignition of the powders below this value being very difficult to achieve.

The incorporation in the proposed propulsive powders of metals or metallic compounds of this type allows the powders to burn in a stable manner at a lower pressure than for propulsive powders not containing them.

These metals and metallic compounds incorporated in the propulsive powders in a finely divided form burn in the combustion gases of the propulsive powders when their temperature is sufiiciently high (the minimum limiting temperature in the case of aluminium being about 2300 K.) and thus increase significantly the energy evolved by the powder.

Also the moderators have the ability to be fixed in an external layer of greater or lesser thickness formed from the grains of powder and thus produce powders of mixed composition (or coated powders), the external composi- Pressure tests [t (initial temperature): 21 0.]

tion having a combustion temperature lower than that of Maximum pressure "bars" 501 the mmmal Core' Deviation of pressures do 45 Consequently by introducing a moderator by means of 5 Number of Shots 10 an operation called glossing into the external layer of a powder grain containing a finely divided metal which is Range tests a good conductor of heat and has a high energy of com- (initial temperature): 31 5o C] bustion, it is possible in the case where the initial powder excluding the metal has a sufficiently high temperature of Velocity at the muzzle 0 Durtaion of velocities rn./s 0.7

combustion, to obtain: Avera 6 ran m 360 An external layer containing both the finely divided S g of if 39 metal and the moderator, and the combustion gases of 131mb of slits 50 which have a sufficiently low temperature (due to the Presence 0 me does not burn (the metal nevertheless preventing ext1n tion by maintaining in the powder hot points at a temperature above the auto-ignition temperature of the powmmdctatot) that me finex divided. meia\ 15 POWDER 'NO 2 Charge used -g. 3.0 Filling coefiicient 0.95

der); this layer has a low energy and since the speed of ability tests tttllitltlllll t 1 w i llll llllllmmmlutm QWPIHM ma e I t f wwpttomtczpwtqlw pctwczcunwcwatt 80 qst)? {p12 slet p92 9 10M and suq s nce we zbceq 0t bGLS'IHLG SIPOAG tpe ante- Runyon :swbewmre or tpc bomqov pA 1112 111159111 1118 11 1pc bomqer pot home 9; 9 {Gillqose U0; PIILU (me were HGAGLIPGIGZZ brcnenqufi cxquc- I2 DLGZGIJGG 0; {p0 moqstsrot) par tpe yne A qpigqeq wary mm E I I 0'52 pstfie neeq "5"" LOAADEK MO 5 0 2 1c usme 9 2n smug/l 10M xewbewmw (q p n U g m q W9 cowpngflolg zbwgq 0; 12113; F i a -Il;] 33g 0 H eyfiersme M ya mews 19m 00 m P W W t i W L my OJ 11mm a 1 2 6 D l all @0111 ill [011 {0 W11. W tic 1115 10 was no augment i 1115p sultan/t0 0{ A 010 m W W m 1/0 1/] not 2 ltltI/J/t {ll/[t at lt/tt [lit Ill/[t/ will 9 8001:] couqnctoz or post yuq p92 5! p18]! cuctlil 0100mt twat M t -tllt 67 (b) as a superficial layer in addition to the metal or metallic compound, from about 0.5% to about 20% by weight of a moderating agent having an imaginary negative apparent potential or low positive apparent potential, said moderating agent being capable of being introduced by a glossing technique and selected from the group consisting of centralites, dinitrotoluenes, camphor, diphenylamine and urethanes, said moderating agent being present in such quantity that the gases produced upon ignition of said powder by the layer containing the moderator have a temperature between the temperature at which there is no stable burning and the temperature above which detonation of the incorporated metal would be produced.

2. A powder according to claim 1 having the following percentage composition by weight:

Percent Nitrocellulose (nitrogen content 13.2%) 92.5 Aluminium powder 5.0 Diphenylamine 1.5 Potassium cryolite 1.0

and 2% by weight of a moderator selected from the group consisting of centralites, dinitrotoluenes, camphor diphenylamine and urethanes which is introduced into the external layer by a glossing technique.

3. A powder according to claim 2 wherein the moderator is ethyl centralite.

4. A powder according to claim 1 wherein the metal is aluminum.

References Cited UNITED STATES PATENTS 3,118,797 1/1964 Coffee l4938 X 3,222,233 12/1965 Matuszko et al. l4938 3,236,704 2/ 1966 Axelrod ct al. l4999 X 

